The present invention relates to a broad band polarizer with a low degree of ellipticity realized in a circular waveguide.
Polarizers are known which make it possible to transform linear polarization into circular polarization and vice versa. For this purpose, they produce a phase difference between two components of the field as a result of electromagnetic paths traversed at different phase velocities. If the two components have the same amplitude and the phase difference produced is .pi./2 the linear polarization is transformed into circular polarization which is called "right" or "left" depending on whether the rotation direction of the field vector does or does not follow the direction of the hands of a watch, when viewing in the propagation direction.
These known polarizers have a circular waveguide, whose inner wall is smooth. A dielectric plate of length L arranged at 45.degree. with respect to the incident linear field vector is associated with said guide. The phase of the field component parallel to the dielectric plate varies by 2.pi.(L/.lambda.d) (.lambda.d: wavelength of the wave considered in the dielectric) in the guide portion of length L incorporating the dielectric plate. In this same portion the phase of the field component orthogonal to the dielectric plate varies by 2.pi.(L/.lambda.g) (.lambda.g: wavelength in the guide). The difference ##EQU1## gives the phase delay of the component parallel to the dielectric plate compared with the component orthogonal to the dielectric plate.
These known polarizers having a smooth waveguide and dielectric plate have two main disadvantages. They are not well suited to working at high power levels and substantial losses occur in the dielectric plate.